Balun transformer

Abstract

To provide a balun transformer with enhanced magnetic coupling between primary and secondary windings.SOLUTION: A balun transformer 1 includes terminal electrodes E1 to E4, coil patterns 10 and 30 connected in parallel between the terminal electrode E1 and the terminal electrode E2, and coil patterns 20 and 40 connected in parallel between the terminal electrode E3 and the terminal electrode E4. The coil patterns 10, 20, 30, and 40 are coaxially laminated in this order. In this way, the coil patterns 10 and 30 forming the primary winding and connected in parallel with each other and the coil patterns 20 and 40 forming the secondary winding and connected in parallel with each other are alternately laminated. Therefore, it is possible to enhance the magnetic coupling between the primary winding and the secondary winding.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a balun transformer, and more particularly to a chip-type balun transformer having a structure in which a plurality of coil patterns are coaxially stacked. [Background technology]

[0002] Usually, a transmission line connected to an antenna or the like is an unbalanced transmission line, whereas a transmission line connected to a high-frequency circuit such as a semiconductor IC is a balanced transmission line. For this reason, when connecting an unbalanced transmission line and a balanced transmission line, a balun transformer that converts between an unbalanced signal and a balanced transmission line is inserted between them. Here, an unbalanced signal refers to a single-ended signal based on a fixed potential (e.g., ground potential), and a balanced signal refers to a differential signal. Patent Document 1 discloses a chip-type balun transformer having a structure in which multiple coil patterns are stacked coaxially. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-260146 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the balun transformer described in Patent Document 1, it is difficult to increase the magnetic coupling between the primary winding and the secondary winding.

[0005] SUMMARY OF THE PRESENT EMBODIMENTS Accordingly, an object of the present invention is to provide a balun transformer in which the magnetic coupling between the primary winding and the secondary winding is enhanced. [Means for solving the problem]

[0006] A balun transformer according to the present invention comprises first to fourth terminal electrodes, first and third coil patterns connected in parallel between the first terminal electrode and the second terminal electrode, and second and fourth coil patterns connected in parallel between the third terminal electrode and the fourth terminal electrode, and is characterized in that the first, second, third and fourth coil patterns are coaxially stacked in this order.

[0007] According to the present invention, the first and third coil patterns which form the primary winding and are connected in parallel to each other, and the second and fourth coil patterns which form the secondary winding and are connected in parallel to each other are alternately stacked, thereby making it possible to enhance the magnetic coupling between the primary winding and the secondary winding.

[0008] The balun transformer according to the present invention may further include fifth and seventh coil patterns connected in parallel to each other and in series to the first and third coil patterns, and sixth and eighth coil patterns connected in parallel to each other and in series to the second and fourth coil patterns, and the fifth, sixth, seventh and eighth coil patterns may be coaxially stacked in this order, thereby making it possible to secure a larger number of turns.

[0009] In this case, the outer circumferential ends of the first and third coil patterns may be commonly connected to a first terminal electrode, the outer circumferential ends of the second and fourth coil patterns may be commonly connected to a third terminal electrode, the outer circumferential ends of the fifth and seventh coil patterns may be commonly connected to a second terminal electrode, the outer circumferential ends of the sixth and eighth coil patterns may be commonly connected to a fourth terminal electrode, the inner circumferential ends of the first and third coil patterns may be commonly connected to the inner circumferential ends of the fifth and seventh coil patterns, and the inner circumferential ends of the second and fourth coil patterns may be commonly connected to the inner circumferential ends of the sixth and eighth coil patterns. This makes it easy to connect the terminal electrodes and the coil patterns.

[0010] The balun transformer according to the present invention further includes a fifth coil pattern connected in series to the first and third coil patterns and a sixth coil pattern connected in series to the second and fourth coil patterns, the outer circumferential ends of the first and third coil patterns are commonly connected to the first terminal electrode, the outer circumferential ends of the second and fourth coil patterns are commonly connected to the third terminal electrode, the outer circumferential end of the fifth coil pattern is connected to the second terminal electrode, the outer circumferential end of the sixth coil pattern is connected to the fourth terminal electrode, the inner circumferential ends of the first and third coil patterns are commonly connected to the inner circumferential end of the fifth coil pattern, the inner circumferential ends of the second and fourth coil patterns are commonly connected to the inner circumferential end of the sixth coil pattern, and the pattern width of the fifth and sixth coil patterns may be wider than the pattern width of the first to fourth coil patterns. This makes it easy to adjust the number of turns and reduces the difference in current density of the current flowing through each coil pattern. Effect of the Invention

[0011] In this way, according to the present invention, it is possible to provide a balun transformer in which the magnetic coupling between the primary winding and the secondary winding is enhanced. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic perspective view for explaining the structure of a balun transformer 1 according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic cross-sectional view for explaining the structure of the balun transformer 1. As shown in FIG. [Diagram 3] FIG. 3 is a schematic plan view for explaining the pattern shapes of the conductor layers L1, L3, L5, and L7. [Figure 4] FIG. 4 is a schematic plan view for explaining the pattern shapes of the conductor layers L2, L4, L6, and L8. [Diagram 5] FIG. 5 is an equivalent circuit diagram of the balun transformer 1. [Figure 6] FIG. 6 is a graph showing the relationship between frequency and coupling coefficient. [Figure 7]FIG. 7 is a graph showing the relationship between frequency and insertion loss. [Figure 8] FIG. 8 is a schematic perspective view for explaining the structure of a balun transformer 2 according to the second embodiment of the present invention. [Figure 9] FIG. 9 is a schematic cross-sectional view for explaining the structure of the balun transformer 2. As shown in FIG. [Figure 10] FIG. 10 is a schematic plan view for explaining the pattern shapes of the conductor layers L1, L3, and L5. [Figure 11] FIG. 11 is a schematic plan view for explaining the pattern shapes of the conductor layers L2, L4, and L6. [Figure 12] FIG. 12 is an equivalent circuit diagram of the balun transformer 2. As shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0014] <First embodiment> Fig. 1 is a schematic perspective view for explaining the structure of a balun transformer 1 according to a first embodiment of the present invention, and Fig. 2 is a schematic cross-sectional view for explaining the structure of the balun transformer 1.

[0015] As shown in Fig. 1 and Fig. 2, the balun transformer 1 according to the first embodiment includes eight conductor layers L1 to L8 laminated in this order, a magnetic body 3 in which the conductor layers L1 to L8 are embedded, and terminal electrodes E1 to E4. The conductor layers L1 to L8 have coil patterns 10, 20, 30, 40, 50, 60, 70, and 80, respectively, and are covered with an insulating resin layer 4. The conductor layers L1 to L8 are embedded in the magnetic body 3 via the insulating resin layer 4. Four terminal electrodes E1 to E4 are exposed from the magnetic body 3. The magnetic body 3 is a composite member containing a metal magnetic filler made of iron (Fe) or a permalloy-based material and a resin binder, and forms a magnetic path for a magnetic flux generated by passing a current through the coil patterns 10, 20, 30, 40, 50, 60, 70, and 80. As the resin binder, a liquid or powdered epoxy resin is preferably used.

[0016] The terminal electrodes E1 and E2 are used, for example, as primary side terminals (unbalanced signal terminals), and the terminal electrodes E3 and E4 are used, for example, as secondary side terminals (balanced signal terminals). In this case, one of the terminal electrodes E1 and E2 constituting the unbalanced signal terminal is connected to an unbalanced transmission line, and the other is connected to a ground wiring. The terminal electrodes E3 and E4 are connected to a pair of balanced transmission lines.

[0017] Coil patterns 10, 30, 50, and 70 arranged on conductor layers L1, L3, L5, and L7 are connected between the terminal electrodes E1 and E2. Coil patterns 20, 40, 60, and 80 arranged on conductor layers L2, L4, L6, and L8 are connected between the terminal electrodes E3 and E4.

[0018] FIG. 3 is a schematic plan view for explaining the pattern shapes of the conductor layers L1, L3, L5, and L7.

[0019] As shown in Fig. 3, the coil patterns 10, 30 included in the conductor layers L1, L3 have their outer peripheral ends 11, 31 commonly connected to the terminal electrode E1. The coil patterns 50, 70 included in the conductor layers L5, L7 have their outer peripheral ends 51, 71 commonly connected to the terminal electrode E2. The inner peripheral ends 12, 32, 52, 72 of the coil patterns 10, 30, 50, 70 included in the conductor layers L1, L3, L5, L7 are short-circuited. The coil patterns 10, 30 are wound counterclockwise (left-handed) from the outer peripheral ends 11, 31 toward the inner peripheral ends 12, 32, and the coil patterns 50, 70 are wound clockwise (right-handed) from the outer peripheral ends 51, 71 toward the inner peripheral ends 52, 72. The relay patterns 33, 53, 73 included in the conductor layers L3, L5, L7 are independent of the coil patterns 30, 50, 70, and are connected to inner circumferential ends 22, 42, 62, 82 of the coil patterns 20, 40, 60, 80 described below. The dummy pattern 13 provided on the conductor layer L1 is provided to prevent steps in this portion on the upper conductor layers L2 to L8.

[0020] FIG. 4 is a schematic plan view for explaining the pattern shapes of the conductor layers L2, L4, L6, and L8.

[0021] As shown in Fig. 4, the coil patterns 20, 40 included in the conductor layers L2, L4 have their outer peripheral ends 21, 41 commonly connected to the terminal electrode E3. The coil patterns 60, 80 included in the conductor layers L6, L8 have their outer peripheral ends 61, 81 commonly connected to the terminal electrode E4. The inner peripheral ends 22, 42, 62, 82 of the coil patterns 20, 40, 60, 80 included in the conductor layers L2, L4, L6, L8 are short-circuited. The coil patterns 20, 40 are wound clockwise (right-handed) from the outer peripheral ends 21, 41 toward the inner peripheral ends 22, 42, and the coil patterns 60, 80 are wound counterclockwise (left-handed) from the outer peripheral ends 61, 81 toward the inner peripheral ends 62, 82. The relay patterns 23, 43, 63 included in the conductor layers L2, L4, L6 are independent of the coil patterns 20, 40, 60, and are connected to the inner circumferential ends 12, 32, 52, 72 of the coil patterns 10, 30, 50, 70.

[0022] In the balun transformer 1 according to the present embodiment, the coil patterns 10, 30, 50, 70 and the coil patterns 20, 40, 60, 80 having the above-mentioned structure are alternately stacked coaxially. Therefore, as shown in FIG. 5 which is an equivalent circuit diagram, the parallel-connected coil patterns 10, 30 and the parallel-connected coil patterns 50, 70 are connected in series between the terminal electrodes E1 and E2, and the parallel-connected coil patterns 20, 40 and the parallel-connected coil patterns 60, 80 are connected in series between the terminal electrodes E3 and E4. Here, the number of turns of each of the coil patterns 10, 30, 50, 70 is 4.5 turns, so that a total of 9 turns of coils are connected between the terminal electrodes E1 and E2. Similarly, the number of turns of each of the coil patterns 20, 40, 60, 80 is 4.5 turns, so that a total of 9 turns of coils are connected between the terminal electrodes E3 and E4.

[0023] Fig. 6 is a graph showing the relationship between frequency and coupling coefficient, and Fig. 7 is a graph showing the relationship between frequency and insertion loss, in which the symbol A shows the characteristics of the balun transformer 1 according to this embodiment, and the symbol B shows the characteristics of a general balun transformer. A general balun transformer has coil patterns 10, 30, 50, and 70 all connected in series, and coil patterns 20, 40, 60, and 70 all connected in series, and the total number of turns of the coil patterns is adjusted to 9 turns to match the inductance value with the balun transformer 1 according to this embodiment.

[0024] As shown in FIGS. 6 and 7, it can be seen that the balun transformer 1 according to this embodiment has a higher coupling coefficient and a lower insertion loss, particularly in the high frequency range, compared to a typical balun transformer.

[0025] In this way, in the balun transformer 1 of this embodiment, the parallel-connected coil patterns 10, 30 and the parallel-connected coil patterns 20, 40 are coaxially stacked in this order, and the parallel-connected coil patterns 50, 70 and the parallel-connected coil patterns 60, 80 are coaxially stacked in this order, making it possible to enhance the magnetic coupling between the coil patterns 10, 30, 50, 70 that constitute the primary winding and the coil patterns 20, 40, 60, 70 that constitute the secondary winding.

[0026] Moreover, since the terminal electrodes E1 to E4 are all connected to the outer circumferential ends of the corresponding coil patterns, the coil patterns can be easily connected to the terminal electrodes E1 to E4.

[0027] <Second embodiment> Fig. 8 is a schematic perspective view for explaining the structure of a balun transformer 2 according to a second embodiment of the present invention, and Fig. 9 is a schematic cross-sectional view for explaining the structure of the balun transformer 2.

[0028] As shown in Figs. 8 and 9, the balun transformer 2 according to the second embodiment includes six conductor layers L1 to L6 stacked in this order, a magnetic body 3 in which the conductor layers L1 to L6 are embedded, and terminal electrodes E1 to E4. The configuration of the conductor layers L1 to L4 is the same as that of the balun transformer 1 according to the first embodiment, and the configuration of the conductor layers L5 and L6 is different from that of the balun transformer 1 according to the first embodiment. Coil patterns 10, 30, and 50 arranged on the conductor layers L1, L3, and L5 are connected between the terminal electrode E1 and the terminal electrode E2. Coil patterns 20, 40, and 60 arranged on the conductor layers L2, L4, and L6 are connected between the terminal electrode E3 and the terminal electrode E4. Since the other basic configuration is the same as that of the balun transformer 1 according to the first embodiment, the same elements are given the same reference numerals and a duplicated description is omitted.

[0029] FIG. 10 is a schematic plan view for explaining the pattern shapes of the conductor layers L1, L3, and L5.

[0030] 10, the pattern shapes of the coil patterns 10, 30 included in the conductor layers L1, L3 are the same as those of the balun transformer 1 according to the first embodiment. The coil pattern 50 included in the conductor layer L5 has an outer peripheral end 51 connected to the terminal electrode E2 and an inner peripheral end 52 commonly connected to the inner peripheral ends 12, 32 of the coil patterns 10, 30.

[0031] FIG. 11 is a schematic plan view for explaining the pattern shapes of the conductor layers L2, L4, and L6.

[0032] 11, the pattern shapes of the coil patterns 20, 40 included in the conductor layers L2, L4 are the same as those of the balun transformer 1 according to the first embodiment. The coil pattern 60 included in the conductor layer L6 has an outer peripheral end 61 connected to the terminal electrode E4 and an inner peripheral end 62 commonly connected to the inner peripheral ends 22, 42 of the coil patterns 20, 40.

[0033] In the balun transformer 2 according to the present embodiment, the coil patterns 10, 30, 50 and the coil patterns 20, 40, 60 having the above-mentioned structure are alternately stacked coaxially. Therefore, as shown in FIG. 12 which is an equivalent circuit diagram, the parallel-connected coil patterns 10, 30 and the coil pattern 50 are connected in series between the terminal electrodes E1 and E2, and the parallel-connected coil patterns 20, 40 and the coil pattern 60 are connected in series between the terminal electrodes E3 and E4. Here, the number of turns of each of the coil patterns 10, 30 is 4.5 turns, and the number of turns of the coil pattern 50 is 2.5 turns, so that a coil with a total of 7 turns is connected between the terminal electrodes E1 and E2. Similarly, the number of turns of each of the coil patterns 20, 40 is 4.5 turns, and the number of turns of the coil pattern 60 is 2.5 turns, so that a coil with a total of 7 turns is connected between the terminal electrodes E3 and E4.

[0034] As illustrated in this embodiment, the balun transformer according to the present invention may have a mixture of coil patterns connected in parallel and coil patterns not connected in parallel. This allows the total number of layers to be reduced and the total number of turns to be easily adjusted. Moreover, in this embodiment, the pattern width in the radial direction of the coil patterns 50 and 60 is wider than the pattern width in the radial direction of the coil patterns 10, 20, 30, and 40, and is about twice as wide. This makes it possible to reduce the difference in current density of the current flowing through each coil pattern. Furthermore, when the coil patterns constituting the primary winding and the coil patterns constituting the secondary winding each have a three-layer structure as in this embodiment, it is difficult to make the total number of turns of each of the primary winding and the secondary winding an odd number in a general balun transformer, but in this embodiment, it is possible to make the total number of turns of each of the primary winding and the secondary winding an arbitrary number.

[0035] Although a preferred embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention, and it goes without saying that these modifications are also included within the scope of the present invention.

[0036] For example, in the balun transformer 1 according to the first embodiment, two coil patterns located on different conductor layers are connected in parallel, but three or more coil patterns located on different conductor layers may be connected in parallel.

[0037] In addition, in the balun transformers 1 and 2 according to the first and second embodiments, the primary winding and the secondary winding have the same number of turns, but this is not essential to the present invention. [Explanation of symbols]

[0038] 1,2 Balun transformer 3 Magnetic element 4 Insulating resin layer 10,20,30,40,50,60,70,80 coil patterns 11,21,31,41,51,61,71,81 Outer edge 12,22,32,42,52,62,72,82 Inner end 13 Dummy Pattern 23,33,43,53,63,73 relay pattern E1~E4 terminal electrode L1~L8 Conductor layers

Claims

1. First to fourth terminal electrodes; first and third coil patterns connected in parallel; second and fourth coil patterns connected in parallel; fifth and seventh coil patterns connected in parallel; sixth and eighth coil patterns connected in parallel; the first and third coil patterns and the fifth and seventh coil patterns are connected in series between the first terminal electrode and the second terminal electrode; the second and fourth coil patterns and the sixth and eighth coil patterns are connected in series between the third terminal electrode and the fourth terminal electrode, A balun transformer, wherein the first, second, third, fourth, fifth, sixth, seventh and eighth coil patterns are coaxially stacked in this order.

2. outer circumferential ends of the first and third coil patterns are commonly connected to the first terminal electrode, outer circumferential ends of the second and fourth coil patterns are commonly connected to the third terminal electrode, outer circumferential ends of the fifth and seventh coil patterns are commonly connected to the second terminal electrode, outer circumferential ends of the sixth and eighth coil patterns are commonly connected to the fourth terminal electrode, the first and third coil patterns have their inner circumferential ends connected in common to the inner circumferential ends of the fifth and seventh coil patterns; 2. The balun transformer according to claim 1, wherein inner peripheral ends of the second and fourth coil patterns are commonly connected to inner peripheral ends of the sixth and eighth coil patterns.

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